if(APP STREQUAL "helloworld")
    add_subdirectory(helloworld)
elseif(APP STREQUAL "shell")
    add_subdirectory(shell)
elseif(APP STREQUAL "stdio")
    add_subdirectory(stdio)
elseif(APP STREQUAL "fatfs")
    add_subdirectory(fatfs)
endif()
